The invention relates to a method of embedding extra information in an input signal.
The invention further relates to a system for embedding extra information in an input signal.
The invention further relates to a method of decoding extra information embedded in an input signal.
The invention further relates to a system for decoding extra information embedded in an input signal.
In a Digital Cinema Theatre, very high quality digital video material, typically 1920xc3x971080, 30-bit RGB, is projected on a large screen. Because of the extremely high video quality, this material needs protection against unauthorized copying. A straightforward way to obtain a copy of the projected video material is by simply using a video camera. Today, content providers are facing the problem that good quality recordings are being made in that way, and that illegal copies of these recordings are being sold.
To fight this form of piracy, it would help if the particular cinema theatre, as well as possibly the projection date and time, could be identified from the illegal recording. Preferably, this theatre information is embedded in a way such that it is not obtrusive, such that it is not annoying to viewers, and such that it cannot be easily removed from the illegal recording.
A straightforward method to prevent the above-described scenario would be the following. At the time of projection, a unique number identifying the particular digital cinema theatre together with the time and date of projection are embedded into the video using some digital watermarking technology. This watermarking application, where users get a unique watermark, is usually called xe2x80x9cfingerprintingxe2x80x9d. In this way, the illegal recording will contain the same watermark. Using a digital watermark detector, the identifier number can be retrieved from a copied tape and the xe2x80x9cnegligentxe2x80x9d theatre can be identified.
However, the demands on the video watermarking technology are extremely high. The camcorder is likely not on axis to the projector and the screen is curved both horizontally and vertically. Hence, non-linear distortions will occur, making watermark detection very difficult. Further, there is also the 3:2 pull-down effect, caused by the different frame rates of the movie projector and the recorder, as well as re-sampling, etc. This makes this method less than optimally suited for this purpose.
It is an object of the invention to provide a method according to the preamble, which can embed the extra information in such a way that it can be reliably detected.
This object is achieved in a method according to the invention which comprises associating groups of one or more candidate frames in the input signal with respective portions of the extra information, and performing for each group an edit operation on the one or more candidate frames of that group in dependence on its associated respective portion. When the input signal has been modified in this fashion, the modifications can later be easily and reliably detected by comparing the input signal against an original version and detecting the performed edit operations on the candidate frames. The extra information preferably is an identifier for the theatre in which the modified input signal is to be shown, so that it can be identified later.
In an embodiment the edit operation comprises one of deleting the candidate frame from the input signal, duplicating the candidate frame in the input signal, inserting a new frame into the input signal before the candidate frame, and inserting a new frame into the input signal after the candidate frame. An advantage of this embodiment is that these edit operations are very easy to detect and virtually impossible to undo when only the edited input signal is available. For instance, if a candidate frame is deleted, this can be detected with a simple frame-by-frame comparison, yet the creator of an unauthorized copy cannot restore the candidate frame.
In a further embodiment the new frame is associated with the extra information. The new frame can, for example, comprise an image identifying the theatre in which the modified input signal is to be shown. This later allows easy identification of the theatre in which the unauthorized copy originated.
In a further embodiment the method further comprises inserting an indicator for the candidate frames into the input signal. Since there is always the possibility that some frames were edited due to external circumstances, for example a bad recording, it is advantageous to identify which frames are candidate frames, so that only those frames are considered in detecting the extra information. By inserting this identification into the input signal, it can be detected later. Preferably the indicator is inserted as a watermark.
In a further embodiment the candidate frames are frames that represent scene changes in the input signal. An advantage of this embodiment is that these frames can be edited with less risk that the rendering will later be adversely affected. For instance, deleting a frame that occurs at a scene boundary will, at worst, only make the scene boundary more abrupt.
It is a further object of the invention to provide a system according to the preamble, which can embed the extra information in such a way that it can be reliably detected.
This object is achieved in a system according to the invention which comprises associating means for associating groups of one or more candidate frames in the input signal with respective portions of the extra information, and editing means for performing for each group an edit operation on the one or more candidate frames of that group in dependence on its associated respective portion.
It is a further object of the invention to provide a method according to the preamble, which allows easy and reliable detection of the extra information.
This object is achieved in a method according to the invention which comprises comparing the input signal with an original input signal to obtain one or more differences between the input signal and the original input signal, and decoding the one or more differences as respective portions of the extra information. Comparing the input signal with an original version, preferably on a frame-by-frame basis, allows for easy detection of those frames that were edited. The nature of the edit operations that were performed, together with the location of the edited frames, can be used to determine the portions of the extra information.
It is a further object of the invention to provide a system according to the preamble, which allows easy and reliable detection of the extra information.
This object is achieved in a system according to the invention which comprises comparing means for comparing the input signal with an original input signal to obtain one or more differences between the input signal and the original input signal, and decoding means for decoding the one or more differences as respective portions of the extra information.